An image forming apparatus of a particular type known in the art includes a plurality of photoconductor drums, a plurality of LED heads (exposure units), and a drum supporting member configured to support the plurality of photoconductor drums and the plurality of LED heads. Each LED head is disposed above a corresponding photoconductor drum, and the drum supporting member at which the plurality of the photoconductor drums and the plurality of LED heads are supported is configured to be movable relative to a body casing of the apparatus. Each LED head is supported by an arm that is swingably provided at the drum supporting member. Each arm is continuously biased upwardly by a spring, so that when the photoconductor drum is moved out of the body casing of the apparatus, the arm is released and swung upward by the action of the spring until it is stopped by a stopper so that the LED head with its light-emitting side facing frontward is retained in a position (retreating position) where it protrudes upward (outside) from the drum supporting member. In this way, each LED head is retreated from the corresponding photoconductor drum so that a cartridge containing the photoconductor drum can be removed easily.